1. Field of the Invention
The present invention relates to a method of activating virtual prepaid cards.
2. Description of the Prior Art
With reference to French patent FR 2750273, a prepaid card enables its holder to receive a service from a service provider, the payment for the service being made in advance when the card is purchased.
A distinction must be made between virtual prepaid cards and non-virtual prepaid cards. For a virtual prepaid card, all the characteristics of the card, and in particular its credit, are managed by a centralized server. For a non-virtual prepaid card, the card itself contains an integrated circuit with a microcontroller that contains all the characteristics of the card, including the remaining credit. The Télécarte (Registered Trade Mark) is one example of a non-virtual prepaid card.
The invention relates only to virtual prepaid cards, which are also known as “virtual tokens”.
Unlike non-virtual prepaid cards, which necessarily include an electronic means in the form of the integrated circuit, virtual prepaid cards can be of two kinds:                non-material virtual prepaid cards, which consist of an identification code, generally a number, which can be read on a scratch card after scratching off a covering, for example, and        material virtual prepaid cards, which consist of a physical device, for example a memory, in which the identification code has been prerecorded.        
The following operations are effected before a virtual prepaid card can be used to access a service:                fabricating the card with an associated identification code,        storing the identification code in an authentication server,        selling the card,        authenticating the purchased card by the server,        providing a service, and        conducting a dialog with the server to enable the service provider to discover the remaining credit and the other parameters of the virtual prepaid card and to update the credit of the virtual prepaid card.        
The user purchases a virtual prepaid card from a distributor-trader. During its fabrication, the card is initially credited with a number of units corresponding to its purchase price. Each unit enables to pay for a non-divisible portion of a service. As a general rule, it can be a monetary unit, a basic charge or a minute of call time, in the case of a telephone service, or any other portion of a service.
The virtual prepaid card is managed by the server, whose function is to update the remaining credit of the card, expressed as a number of units, and complementary data such as expiry dates, cancellation, etc.
To obtain a service from the service provider, the user must first prove that he is in possession of a virtual prepaid card. For this purpose the server authenticates the card.
The form of authentication described in U.S. Pat. No. 5,991,413 verifies the validity of a sequence of symbols sent to the server:                for non-material virtual prepaid cards, this sequence is the card identification code, which the user communicates to the server via a terminal means, and        for material virtual prepaid cards, on each activation by the user, a different sequence of symbols constituting an identification code is computed cryptographically by the integrated circuit in the card; the integrated circuit can send it either to the server itself or only to the terminal means, which forwards it; this constitutes a secure authentication method.        
If the authentication of the user's virtual prepaid card succeeds, the server indicates the credit remaining on the card to the service provider. This information can optionally be transmitted to the user.
The service provider can then, via the server, debit the user's account as a function of the service provided. The account can be debited before providing the service, or when the service is provided, or after the service has been provided, or by any combination of the above methods.
It is noticed that the service provider is not informed of the purchase of a virtual prepaid card. The service provider must therefore consider a virtual prepaid card to be usable throughout the period during which it is potentially on sale, i.e. in the stock of the service provider, then that of the distributor, and finally at the point-of-sale.
Neither the service provider prior to delivery to the distributor nor the distributor prior to the sale of the card is protected from theft of the virtual prepaid card, i.e. either from theft of the material support or simpler of the identification code in the case of a non-material virtual prepaid card; or from theft of the card in the case of a material virtual prepaid card.
The main drawback of state of the art is therefore that a stolen virtual prepaid card provides entitlement to the service on the same grounds as a virtual prepaid card acquired legitimately.
U.S. Pat. No. 5,903,633 proposes to prerecord a control code with a conventional Personal Identification Number (PIN) code in a telephone card having a magnetic stripe, the codes being partly visible on the card and partly obscured and readable only after scratching off a covering. Before the card retailer sells or otherwise transfers the card to the end user, a point-of-sale terminal transmits the control code to a centralized computer. To validate the purchase of the card and instruct the billing of the card to the retailer in an invoicing computer, the database in the centralized computer verifies the correspondence between the control code and the telephone number of the retailer's terminal. The user having the purchased card can then use the prepaid telephone card in a telephone set in the conventional way, after entering the PIN code.
Although the prior verification of the control code prevents fraudulent use of the PIN code, it requires each retailer to be provided with a terminal that can read the control code and transmit the control code to a specific centralized computer. Furthermore, anyone can find out the control code before purchasing a card, which is an incitement to fraud.